1. Field of the Invention
The present invention relates to composite wheel assemblies for vehicles having an overlay permanently attached to a wheel disc with a combination of adhesives and, particularly, to an improved apparatus and process for permanently attaching an ornamental overlay to the wheel using nests to locate and support the overlay to the wheel creating a mold into which foam can be injected.
2. Description of the Prior Art
Decorative overlays are widely used to enhance the aesthetic appearance of automotive wheels. Overlays are not only employed to improve the appearance of unadorned standard steel wheels, but are also used with cast aluminum wheels, that are known to be expensive and difficult to plate with chromium. Numerous structural combinations of overlays with chrome-plated outboard surfaces have attracted great interest from vehicle manufacturers, because they are lightweight, aesthetically pleasing and offer designers complete flexibility with regard to the aesthetic effect that can be created for a specific vehicle regardless of whether these vehicles use steel or aluminum wheels.
In the past most overlays were mechanically attached to the wheel. For example, Kapanka, U.S. Pat. No. 3,575,468, teaches the use of a spring retention device wherein a joined annular wire spring provides a plurality of outer cover-engaging segments adapted to be secured to a wheel cover at spaced peripheral portions. A plurality of axial segments interconnect the outer cover engaging segments with outer wheel-engaging segments adapted to engage a groove in the rim of the wheel. Stay et al., U.S. Pat. No. 4,895,415; Patti, U.S. Pat. No. 4,950,036; as well as Hudgins et al., U.S. Pat. No. 5,181,767, teach, alternatively, retention of the wheel cover by providing wheel cover retaining means for releasably coupling to at least one lug stud with appropriate configurations enabling releasable coupling between the retainer and at least one stud. German Patent 2,813,412also mechanically attaches the overlay to the wheel by utilizing cavities or undercuts in the face of the wheel. Further, German Patent 2,848,790 also teaches mechanical attachment of the wheel cover to the wheel through the use of clamps so that the cover can be removed for the purpose of cleaning.
Others are adhered to the outboard surface of the wheel, as illustrated by U.S. Pat. No. 3,915,502 to Connell, that teaches an annular-shaped wheel cover that is permanently attached to the wheel with double-sided adhesive tape. The adhesive tape is positioned midway between the rim and the center hub area of the wheel, while the remainder of the wheel cover is spaced apart from the outboard surface of the wheel. Connell positions the adhesive tape at radially outward portions of the wheel in order to avoid the deleterious effects of heat generated by the tire, wheel and brake. While some pressure-sensitive adhesive tapes can be effectively used in temperatures up to 500xc2x0 F. (260xc2x0 C.), the cost of such adhesive tapes is generally prohibitive for use in mass production applications such as securing an overlay to a wheel. Consequently, such applications are generally limited to the use of less expensive adhesive tapes that have relatively low maximum operating temperatures, necessitating that their placement be restricted to the radially outward surfaces of the wheel. Unfortunately, doing so severely limits the adhesive tape""s ability to reliably adhere the overlay to the wheel. Further, the use of adhesive tape because of its defined thickness creates a void between the overlay and the wheel that can collect dirt and debris that may affect the balance of the wheel.
To avoid such problems, as well as to avoid noise problems associated with the use of overlays, the prior art proposes the use of a urethane foam and a method of permanently attaching a plastic cover to a metal wheel through the use of a urethane foam adhesive, that effectively holds the cover in place, closes the void between the overlay and the wheel, and reduces noise as well as provides adequate theft deterrence. This method is best described in U.S. Pat. No. 3,669,501 to Derleth. The process disclosed in Derleth is an annular-shaped overlay composed of a thin plastic cover formed from acrylonitrile-butadiene-styrene (ABS) mounted to a wheel spider. The overlay is configured to have variations in contours in a direction transverse to the axis of the wheel that exceed the variations in the rim and/or disc contour of the wheel, which variations would be extremely difficult and expensive, if not impossible, to stamp or draw in the disc of the wheel. During assembly, a foamable polyurethane adhesive is coated on the wheel, and the cover is then quickly clamped to the wheel before the polyurethane begins to foam. As such, the void between the wheel and cover is filled with the polyurethane foam. However, any excess polyurethane foam formed around the bolt holes or at the periphery of the assembly surrounding the axle hub will squeeze out if appropriate sealing provisions are not made.
One obvious shortcoming of the process disclosed by Derleth is that the composite wheel must be imperforate, except for the small bolt openings necessary for attaching the wheel to a vehicle. It is understood by those skilled in the art that it is necessary to avoid the deleterious effects of heat generated by the wheel and brake, that cause the ABS plastic overlay to distort, cause delamination of any surface treatment, i.e. paint, plating, etc., and further cause the foam adhesive to degrade, distort and eventually melt. Further problems with urethane formed wheels surfaced in use. These wheels were very heavy due to the high density of the foam and variation in localized density during the manufacturing phase resulted in severe wheel imbalances.
Turbine openings are a necessary element in today""s wheel systems in providing proper cooling to the brake system, not to mention the aesthetics of endless configurations of turbine openings that add individuality and style to a vehicle. Any opening in the wheel or overlay using the process disclosed in Derleth is a pathway for the foam mixture to escape when it begins to foam and/or cure. Larger openings, such as turbine openings, would not be possible using the Derleth process without additional structure to seal the openings to prevent the foaming material from escaping.
It is appreciated by those skilled in the art that it is advantageous to completely fill the cavity with foam adhesive to acoustically dampen any sound produced when the overlay is struck. A drawback of the process according to Derleth is that excess foam mixture is required to ensure that the cavity between the cover and the wheel is completely filled after the material vents out through the bolt openings. The process disclosed by Derleth requires any substantial opening in the wheel be plugged or sealed with a sleeve to prevent foam leakage. For example, if the wheel hub was left unsealed it would provide a path for some of the foam to escape, and the security of the cover could be jeopardized. Further, all of the excess foam must be manually removed, which adds significant cost to the process.
A further disadvantage of the process of Derleth is that the polyurethane foam adhesive completely breaks down at high temperatures, particularly in the immediate region of the wheel hub where temperatures tend to be much higher than in the remainder of the wheel.
The method according to Derleth has been known since the early 1970""s and due to its many disadvantages has yet to realize practical applications and commercial success. The process cannot accommodate the application temperature requirements, the need for lighter weight components, and degradation of the urethane adhesive over time, as well as the need for turbine openings in the outboard face of the wheel. Further, the process is extremely costly due to the labor intensive trimming operations, difficult process control, environmental, health and safety concerns.
The teachings of Beam, U.S. Pat. Nos. 5,368,370 and 5,461,779, of a full surface curable adhesive are prohibitively expensive and wasteful since there is no need for a full surface uniform layer of adhesive to hold the overlay to the wheel. Further, a full surface uniform layer of curable adhesive also detrimentally affects the balancing considerations of the wheel and overlay assembly.
To avoid the problems of Beam, U.S. Pat. No. 5,597,213 to Chase, assigned to the assignee hereof, teaches the use of an intermediate positive fixing element for temporarily positioning and securing an overlay to a wheel during an interval in which a selectively positioned or applied adhesive required to permanently adhere the overlay to the wheel is allowed to cure. The adhesive is selectively placed between the overlay and the wheel to alleviate concerns of squeaks and rattles as well as to improve the overall manufacturability, performance and consumer-perceived quality of the resulting wheel assembly. The requirement of an intermediate positive fixing element not only adds costs to the overlay but requires careful handling and special packaging, all adding to the overall cost of the assembly.
Understandably, what is needed is an economical overlay apparatus and method for assembling such overlay to an automotive steel or alloy wheel, in which the method promotes the ability to accurately position and reliably permanently secure the overlay to the wheel by the use of selective application of a costly curable adhesive in combination with a less expensive foam adhesive so as to improve the manufacturability of the wheel, reduce the cost of manufacturing and not detrimentally affect wheel balance or performance.
The present invention provides a cost effective, highly efficient, safe process for permanently attaching an overlay or cladding to a wheel. The wheel has severe surface variations due to manufacturing tolerances. In addition, the overlay has its own surface variations due to manufacturing tolerances. When the overlay is attached to the wheel, these tolerances are stacked, and could result in an even larger variation. These stacked tolerance variances must be taken into consideration during the foaming process. If the variances are not properly accounted for, one of two things will happen. Either too much foam will be injected into the cavity and foam will flash out through any opening between the wheel and the overlay, as seen in the Derleth process, requiring trimming, or not enough foam will be injected into the cavity resulting in voids and inadequate cover retention. In the present invention, a sealant bead is generally applied along the outer periphery or diameter of the overlay. Optionally, a sealant bead may be applied around the turbine openings and/or inner diameter or periphery, to provide additional sealing and completely eliminate foam flashing, that in turn eliminates the step of trimming excess foam from any adjoining surfaces between the cladding and wheel after the adhesive/sealant has cured.
In the present invention, the overlay is aligned with, located, and clamped to the wheel with the exception of predetermined sealed areas. The outboard surfaces of the overlay and wheel are spaced apart, leaving a cavity therebetween. Localized nests at strategically placed locations act on the wheel and overlay assembly to seal the assembly on the wheel and thereby create a mold cavity. Net standoffs may be used to assist locating the cover with respect to the wheel and the localized nests interact with the overlay and wheel assembly to create a mold cavity between the overlay and the wheel into which the liquid foam is injected and allowed to react to fill the cavity.
A sealant or adhesive can be applied to the overlay prior to assembling the overlay to the wheel, depending on the type of wheel that is used to create the composite wheel assembly. If an adhesive/sealant is applied, the process begins by fixturing the overlay. In the present invention the overlay is oriented with the outboard face down in a nest or fixture. The overlay is located radially off the outside or inside diameter, circumferentially off the valve stem opening or turbine openings and axially off the outboard surface rim flange area. Vacuum may be applied to the cladding, if necessary, to remove any warpage and assure a truer inboard surface for adhesive or sealant application. Alternatively, the cladding may be fixtured and clamped to ensure the various locator datums are maintained. An adhesive/sealant is selectively applied to the cladding at preselected locations depending on the application. The sealant is applied to the surface of the overlay or the wheel before the cladding is joined to the wheel. Typically, the sealant will be applied to the outer diameter or peripheral edge of the overlay and, alternatively, as needed, the inner diameter or hub opening as well as surrounding the turbine openings. The adhesive/sealant can be applied to other areas for additional cladding adhesive strength/sealing or to direct the foam flow pattern. A robotic applicator system is used.
With the cladding appropriately fixtured, as disclosed above, the cladding is located on the wheel. It is preferable to locate axially off the tire side of the outer wheel flange or rim flange, radially off the tire side rim flange and circumferentially off the turbine openings or valve stem. The hub bore, bolt circle and other details can also be used depending on how the wheel is manufactured and the relationship of the datums to one another and to the overlay. The overlay is located in a fixture that locates and processes the cladding to the wheel. An optional clamping system is applied to the assembly following preheating of the assembly. The clamping system consists of temporary clamps, such as toggle clamps, to hold the overlay to the wheel until further processing steps are completed. Also, intermediate attachment and locating features can be used to hold the cladding to the wheel while the adhesive/sealant sets, if an adhesive is used.
At this point, if a sealant/adhesive is used, it may require additional curing. In such a case, the wheel and overlay assembly is transferred to a curing station, where the sealant/adhesive is allowed to cure. Depending on the type of adhesive/sealant used the curing may involve a chemical reaction in case of a two component adhesive, or heat or UV exposure to enhance the reaction and cure time of the adhesive/sealer before the clamping system is applied. Further conditioning of the assembly can also take place in the curing station.
After the adhesive/sealant has cured, or if no sealant is used, the wheel and overlay assembly is preheated. The preheating is necessary to raise the surface temperature of the assembly to a defined temperature that enhances foam initiation time, adhesion, gel, cohesion, filling, and resultant mechanical properties of the foam.
The preheated assembly is then placed in a filling station that consists of a clamping fixture having various nests and a foam metering unit. The wheel and cladding assembly enters the filling station with the wheel located outboard face down against the inboard side of the cladding and the pallet on which it travels is engaged by a lower moving platen that rises and clamps the wheel assembly and associated pallet between the lower and upper platen of the filling station fixture. A first set of nests, that may be made from a variety of materials depending on their function, engages predetermined areas of the cladding and wheel assembly from the bottom so as to conform to substantially the outboard surface of the cladding to support the cladding during the high pressure phase of the foam filling. A center bottom nest generally conforms to the inside diameter of the cladding and axle shaft opening of the wheel to provide a seal thereto. Optionally, a second set of nests independently seal the various turbine openings allowing independent movement to self-locate to the cladding and wheel. The various nests independently engageable in combination with the steel wheel and cladding create a mold in which the foam can be injected. A metering unit is used to accurately mix and dispense the two component urethane foam. A nozzle mounted to the top clamp platen engages a fill port in the back side of the wheel to inject the foamable material in the cladding/wheel assembly cavity. The lower and upper platen clamp is held closed for a predetermined time while the foam flows, gels and thereafter fills the cavity. Thereafter the turbine openings, if used, center bottom and valve stem nests are disengaged and the lower and upper platen clamp is released to allow the pallet containing the cladding and wheel assembly to be moved to the next station for curing, and eventual removal from the fixture. A low out of round point is identified on the wheel assembly before it is shipped.
In summary, the wheel, overlay and selective application of the localized nests of the present invention create a sealed mold of the cavity between the wheel and the overlay for the foam to expand in to. The nests and the sealant bead, in combination with the clamping system, provide adequate sealing to prevent foam from escaping through any of the openings in the wheel disc. There is no need to add sleeves and covers, trim away excess foam from the wheel assembly, or clean up any foam scrap from the manufacturing equipment and area.
In another embodiment of the present invention, a vacuum can be applied to the cavity between the overlay and wheel during the foam filling process. Applying the vacuum has a dual purpose of providing additional holding force between the overlay and the wheel disc to prevent the pressure from separating the two elements, and assisting in filling the cavity, thereby eliminating voids.
It is an object of the present invention to provide an improved method of permanently attaching a chrome-plated overlay to any wheel disc with an adhesive. The improved process increases process control capabilities, improves product quality, and reduces environmental, health and safety concerns.
It is a further object of the present invention to use the improved process to permanently attach an overlay to a wheel having turbine openings, without the need for labor intensive trimming of excess foam, or the additional structure of sleeves and covers to seal the openings.
It is yet another object of the present invention to create a mold from the overlay, wheel, and localized nests that adequately seals any voids between the wheel and overlay and after the application of a sealer allows foam to be injected into the void, permanently attaching the overlay to the wheel, without the need to trim excess foam.
It is yet another object of the invention to provide an improved composite wheel chrome-plated overlay that utilizes a foamed adhesive in combination with a predisposed sealer to attach the chrome-plated overlay to any type of wheel and to seal all the interfaces between the overlay and the wheel so as to permanently attach the overlay to the wheel without the need of using excessive foam adhesive that must be cleaned from the composite wheel and overlay assembly prior to use on a vehicle.
It is yet a further object of the present invention to engage localized nests in predetermined timed sequence that seal the openings in the wheel and overlay assembly while allowing foam to completely fill the void between the wheel and overlay without escaping from the openings.